Came into Helsinki for a 3-day visit with no firm plans on what I was going to do, so I looked for something around the central railway station as that is usually a good bet in Europe.
After comparing options the HI seemed to have best combination of location and price/room type for what I wanted. I wasn't eager to stay at an HI as I think of it as an extension of American mediocrity, but I went with it in spite of my feelings. I booked an Executive King. Since I arrived just before the Summer Evening Holiday (when everyone leaves town for summer homes) the price actually went down 30% over the course of my stay (Tue-Fri).
The hotel is right on the square looking at the train station and the airport bus stops 50 metres away from the front door. The trams (most of them) stop in front of the train station and buses are all over, so transportation choice depends on where you are going!
The room was clean, good-sized, nice Scandinavian beds, internet available, and water bottle were free since it was an "executive" room.
Noise was not a problem and I slept OK. Didn't use the restaurant since brekkie wasn't included.
I recommend this as an option if you are coming, just overlook the HI branding and it looks like any other European hotel.